Abstract
A paraffin wax was shape stabilized with 10 wt % of carbon nanotubes (CNTs) and dispersed in various concentrations in an epoxy resin to develop a novel blend with thermal energy storage capabilities. Thermogravimetric analysis showed that CNTs improve the thermal stability of paraffin, while differential scanning calorimetry showed that the paraffin kept its ability to melt and crystallize, with enthalpy values almost proportional to the paraffin fraction. In contrast, a noticeable loss of enthalpy was observed for epoxy/wax blends without CNTs, which was mainly attributed to the partial exudation of paraffin out of the epoxy matrix during the curing phase. Dynamic mechanical thermal analysis contributed to elucidate the effects of the melting of the paraffin phase on the viscoelastic properties of the epoxy blends. Flexural elastic modulus and strength of the blends decreased with the wax/CNT content according to a rule of mixtures, while flexural strain at break values deviate positively from it. These results show the potentialities of the investigated epoxy blends for the development of multifunctional structural composites.
Highlights
Thermal energy storage (TES) consists in storing excess heat and releasing it where and when needed, filling the gap between thermal energy demand and supply
An epoxy matrix was blended with a carbon nanotubes (CNTs)-confined paraffin at different concentrations, and the microstructure and physical properties of the resulting materials were investigated
Paraffin containing a CNT weight fraction of 10 wt % was ground to obtain a powder, and Differential scanning calorimetry (DSC) analysis showed that CNT addition did not noticeably decrease the melting and crystallization enthalpy with respect to the pristine paraffin wax
Summary
Thermal energy storage (TES) consists in storing excess heat and releasing it where and when needed, filling the gap between thermal energy demand and supply. Accumulating and releasing latent thermal energy of organic phase change materials (PCMs) is effective, as these materials can store a large amount of heat per unit mass over a narrow temperature range, with limited volume variations [1,2]. The most widely used organic PCMs are paraffin waxes, poly(ethylene glycol), and fatty acids [3]. In spite of their advantages over other PCMs, they all display confinement problems when heated above their melting temperature and a relatively low thermal conductivity [4]. If the shape stabilization is performed with a thermally conductive structure, such as a carbonaceous nanofiller, the problem of the low thermal conductivity can be partially reduced and the overall thermal exchange improved [2,9,10]
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